EP0428760A1 - Process and apparatus for the manufacture of nets of hot melt adhesive powder on a transfer sheet - Google Patents

Abstract

A process and an apparatus for the manufacture of nets of hot-melt adhesive powder on a transfer sheet and hot-melt adhesive nets produced thereby. In the case of this process, first of all the hot-melt adhesive powder is introduced by means of a doctor blade into the network-like engraving (7) of a rotating engraved roll (6) and is transferred from there onto the transfer sheet (1) passed partially around the engraved roll and in contact with the latter. In this operation, this transfer sheet is previously passed partially around a rotating heating roll (4) and is pressed by means of this heating roll against the surface of the engraved roll, as a result of which the transfer sheet is heated to a temperature above the beginning of melting of the melting powder. According to the invention, fine powder having at most 10 % grain fractions of 100 mu m grain size is used for introducing by the doctor blade into the engraving (7) of the engraved roll (6), which fine powder is set in a rotational motion about an axis parallel to the axis of the engraved roll immediately before being introduced by the doctor blade into the engraving. Furthermore, the transfer sheet (1) is elastically pressed by means of an elastic surface (5) of the heating roll (4) against the engraved roll (6) and, as a result, the fine powder introduced by the doctor blade into its engraving (7) is further compacted. <IMAGE>

Description

The invention relates to a method and a device for producing nets from hot-melt adhesive powder on a transfer carrier web and hot-melt adhesive networks produced therewith. The invention is based on a method described in DE-PS 17 71 516 and DE-OS 25 36 911, in which the hot-melt adhesive powder is first squeegee-coated into the mesh-shaped engraving of a rotating engraving roller and from there onto the partially around this engraving roller with contact with it guided transfer carrier web is transmitted. This transfer carrier web is previously guided around a rotating heating roller and pressed against the surface of the engraving roller via this heating roller, as a result of which the transfer carrier web is heated to a temperature above the start of melting of the melt powder.

After the sintering of the hot-melt adhesive powder, the hot-melt adhesive network produced on a transfer carrier web with these known methods can be removed from the transfer carrier while maintaining its connection and can be used for its intended use later.

So far it has not been possible to use the powder point coating process of the aforementioned type to provide coherent and defect-free hot melt adhesive networks to produce, even if the production of such adhesive networks according to this method has been described in DE-PS 25 36 911. Instead, in the manufacture of the hot-melt adhesive nets that were previously on the market, melt-melt compositions melted by extruders are fed through a heated slot nozzle onto an engraving roller and knife-coated into the mesh-shaped engraving of this engraving roller. The transfer carrier web guided over this engraving roller connects to these hot-melt adhesive masses in the engraving, after which the engraving fillings are pulled off from the engraving roller together with the carrier web after they have cooled.

This known method has a number of disadvantages. First of all, the temperature control, the metering of the hot-melt adhesive mass from the slot nozzle, the doctoring of the mass emerging from the nozzle, the connection of the mass to the carrier web and the joint removal of the carrier web and adhesive network from the engraving roller are difficult to handle. When using thermally unstable hotmelt adhesive compositions, for example copolyamide hotmelt adhesives, intensive cracking up to charring can occur in particular when the coating machine is at a standstill and when starting up. Larger material losses are unavoidable. The hot-melt adhesive granules used must also be almost completely water-free in order to avoid disruptive foaming in the melt. It is also possible to use only very specifically selected hotmelt adhesive compositions with a comparatively low melt viscosity and, moreover, it is often necessary for the hotmelt adhesives to be thermostabilized by addition of stabilizers against cracking. In order to avoid excessive material losses and to be able to maintain satisfactory production, the production must be carried out over days run continuously with one and the same adhesive without being able to switch to another type of hot melt.

The invention is therefore based on the object of providing a powder dot coating process of the type mentioned at the outset, with which continuous and trouble-free hot melt adhesive networks can be produced with ease of handling, with a risk of cracking being avoided with complete certainty, no special hot melt adhesive properties being necessary and in which quickly and without every loss of material can be switched from one type of hot melt to another.

This object is achieved according to the invention in a method of the type mentioned at the outset by using fine powder with a maximum of 10% grain contents of more than 100 μm grain size for wiping into the engraving of the engraving roller, which fine powder rotates about an axis immediately before wiping into the engraving is offset parallel to the engraving roller axis, and that the transfer carrier web is pressed elastically against the engraving roller by means of an elastic surface of the heating roller, and the fine powder that is knife-coated in its engraving is thereby further compressed.

A fine powder is preferably used in this process, the grain fractions with a grain size of less than 90 microns is at least 95%. The grain sizes of up to 150 or 200 .mu.m commonly used in the previously known powder spot coating processes are unusable for solving the problem on which the invention is based and do not produce a coherent network.

By rotating the fine powder around an axis parallel to the engraving roller, the fine powder is compacted immediately before it is introduced into the engraving, so that the fine powder can completely fill the mesh engraving in the engraving roller. This is the case even with fine powders with a small grain size that do not have sufficient flow properties. This rotational movement can be generated with a stir bar, which is arranged horizontally and parallel to the doctor blade edge and rotates continuously. The stirring rod can expediently have staggered pins in close succession, which project approximately radially from the stirring rod circumference and are fastened in bores in the stirring rod. The pen tips should have a minimum distance of 0.5 to 3 cm to the squeegee edge.

In the method according to the invention, i.a. Hotmelt adhesive compositions based on copolyamides, copolyesters, polyethylenes (low and high pressure polyethylene), polyvinyl acetates and / or polyethylene vinyl acetates are used. The properties of the hotmelt adhesive compositions used can vary within a wide range without causing coating problems. The start of melting of the adhesive masses can be very different and can range from 70 ° to 160 ° C. However, hot-melt adhesives that begin to melt in the range from 80 ° to 135 ° C. are particularly suitable.

The melt viscosity can also show significant changes. For example, the melt index of the fine powder used in the process according to the invention at 160 ° C. and with a load on the measuring nozzle of 2.16 kg according to DIN 53735 can be in the range of 1-200 g / 10 min. Hot melt adhesives with a melt index of 5-100 g / 10 min are preferably used.

With the method according to the invention, a high compression of the hot-melt adhesive powder in the engraving of the engraving roller can be achieved, as a result of which interference-free adhesive nets can be generated, which can be easily removed from the transfer carrier while maintaining their connection.

A kraft paper with a strength of 45 to 85 g / m² with a weak silicone coating on one side that is not closed to form a film is suitable. Such paper can completely take over the reticular engraving filling and also allows the melt adhesive net formed on it to be easily separated. The adhesive nets formed on the transfer carrier are always unchanged from the initial powder state. If optically pure powders are used, the adhesive network has retained the optical purity without any tendency to crack. The mesh engraving of the engraving roller is expediently provided with a release film coating, so that an absolutely clean removal of the powder filling compacted in the engraving is ensured. This release film coating can be arranged not only on the mesh engraving, but also on the entire jacket of the engraving roller. A film cover made of baked Teflon has proven particularly useful for this.

The elastic surface of the heating roller can, for example, consist of a temperature-resistant fabric that is wrapped tightly around the heating roller in three to six layers. Such fabrics are, for example, those made from aramids (aromatic polyamides from aromatic diamines and arylene dicarboxylic acids). In addition to fabrics, other flat structures made of temperature-resistant fiber material, for example knitted fabrics, nonwovens, felts, are also suitable. Likewise is a Rubber cover made of temperature-resistant material, for example a vulcanized silicone rubber cover provided with thermally conductive fillers can be used. Suitable fillers are those with high thermal conductivity, such as metal powder, metal oxide powder, carbon black and the like. The elastic surface of the heating roller, which presses the transfer carrier into the powder fillings of the mesh engraving of the engraving roller and brings about a considerable compression of this powder filling, can have a thickness of 1 to 10 mm.

The compaction of the adhesive powder to be introduced into the engraving of the engraving roller can be further improved by an edge bevel grinding of the coating doctor, which is approximately tangential to the engraving roller, which creates a funnel-shaped, tapering gap between the coating doctor edge and the roller surface for the supply of the hot-melt adhesive powder to the roller surface.

The adhesive nets produced by the method according to the invention can be used, for example, in 0.8 to 2 cm wide tapes, with or without transfer carriers, cut in the textile industry, for example for seam sealing or hem production in the production of outer clothing, such as jackets or the like. The net can be ironed onto the outer fabric of the garment together with the transfer carrier with the iron, whereupon the transfer carrier can be pulled off the ironed-on net. The edge of the outer fabric can then be folded over and fixed in its folded position as a hem by ironing again.

However, it is also possible to remove the adhesive nets produced according to the invention after the To use transfer carrier for other different purposes. Since the method according to the invention also permits processing highly viscous enamel compositions with a relatively high melting point to form adhesive networks, it can be used to produce laminations which require increased thermal resistance. The separated web-shaped transfer carrier can be used several times for coating.

However, the method according to the invention can also be used in the processing of hot-melt adhesive compositions which chemically cross-link with prolonged exposure to elevated temperatures and thereby lose their hot-melt adhesive properties. While such hotmelt adhesive compositions can already be processed in the extruder to form non-flowable compositions and therefore not adhesive nets, the flowability of the adhesive nets which can be produced by the process according to the invention is retained even after their completion. The adhesive nets produced with the method according to the invention are therefore suitable for applications which place particularly high demands on temperature resistance which cannot be achieved by non-crosslinking hotmelt adhesives.

The method according to the invention is described below on the basis of a particularly advantageous embodiment of the device used to carry it out, which is shown schematically in the drawing.

• Fig. 1 einen Querschnitt durch diese Vorrichtung;
• Fig. 2 in Abwicklung in vergrößertem Maßstab die netzförmige Gravur auf der Gravurwalze dieser Vorrichtung, wobei die Umfangsrichtung der Gravurwalze mit Pfeil angegeben ist;
• Fig. 3 in Schrägansicht den Rührstab dieser Vorrichtung.

It shows:

• 1 shows a cross section through this device.
• Figure 2 in development on an enlarged scale, the net-shaped engraving on the engraving roller of this device, the circumferential direction of the engraving roller is indicated by an arrow.
• Fig. 3 in an oblique view the stir bar of this device.

In the device shown in FIG. 1 of the drawing, the transfer carrier web 1 is first fed in the direction of the arrow to a deflection roller 2 and then guided around the preheating roller 3. From there, the transfer carrier web reaches the heating roller 4, which is pressed with its elastic coating 5 onto the engraving roller 6, which is equipped on its surface with a mesh-shaped engraving 7, as shown on an enlarged scale in development in FIG. 2.

After the transfer carrier web has been partially passed around the heating roller 4 and then also partially around the engraving roller 6, it is pulled off from the surface of the engraving roller 6 together with the adhesive network applied to it by means of a further deflecting roller 8 and passed past an infrared radiator 9, then partially passed around a cooling roller 10 and finally wound up on a winding roller to form a winding 11.

To fill the mesh engraving 7 on the lateral surface of the engraving roller 6, a powder box 12 is arranged above the engraving roller, which has at its lower exit end a squeegee 13 abutting on the lateral surface of the engraving roller. The fine powder 14 located in the powder box 12 is set in rotation immediately before it emerges from the powder box by a stirring rod 15, which is on its circumference offset radially projecting pins 16 carries (see Fig. 3) and is rotatable about its axis which extends parallel to the axis of the engraving roller 6.

The fine powder 14 thus set in rotation and thus precompacted is spread into the net-shaped engraving 7 of the engraving roller 6 by means of the doctor blade 13 and further compacted in the process. By rotating the engraving roller 6 in the direction of the arrow, the fine powder filled into the engraving reaches the heating roller 4, where it comes into contact with the transferred transfer carrier web 1, which has been heated by the heating roller. By pressing the heating roller 4 with its elastic surface onto the transfer carrier web which is guided over the engraving roller, the fine powder located in the mesh engraving 7 is brought to adhere to this web with renewed compression and sintering, so that the fine powder in its mesh-shaped form given by the engraving 7 Structure can be removed from the engraving roll together with the transfer carrier web and subjected to further sintering and solidification by passing the infrared radiator 9. The detachment of the powder fillings from the mesh engraving 7 is facilitated in that the mesh-shaped engraving 7 of the engraving roller 6 is provided with a separating film coating.

Some exemplary embodiments are described in detail below:

example 1 Production of a hot melt adhesive network that cannot be crosslinked under the influence of temperature.

Engraving roller used with diamond mesh engraving

Diamond angles 60 ° and 30 ° (see Fig. 2)
Engraving width of a diamond leg: 0.6 mm
Diamond thigh length: 2.4 mm
Engraving depth: 0.24 mm

Hot melt adhesive powder used:

Copolyamide powder with the trade name Vestamelt 750 Pl (manufacturer: Hüls company)
Grain distribution:
> 90 µm 0.2%
> 63 µm 28.4%
> 45 µm 49.4%
<45 µm 50.6%
Start of melting: 95 - 100 ° C
Melt index (165 °, 2.16 kp load): 25 g / 10 min according to DIN 53735.

Heating rollers used:

Non-pressed preheating roller (3) and pressed heating roller (4) with elastic cover.
Temperature of both heating rollers: 240 ° C
Covering the heating roller: 6 fabric layers made of an aramid of the trade name "Nomex", each with 200 g / m² in plain weave
Engraving drum temperature: 35 ° C
Coating speed: 25 m / min
Doctor blade: tangent to the engraving roller
Doctor blade thickness: 0.6 mm
Doctor blade width: 40 mm
Edge grinding: 45 degrees

Transfer carrier used:

Silicon paper 55g / m²
Weight of the hot-melt adhesive network obtained: 40 g / m².

Example 2 Production of a hot melt adhesive network which can be crosslinked under the influence of temperature: Engraving roller used with diamond mesh engraving:

as in example 1

Hot melt adhesive powder used:

90% by weight copolyamide powder of the trade name Vestamelt 250 / Pl (manufacturer: Hüls company)
10% by weight polyisocyanate ITDI-T1890 powder (= polyisocyanate based on isophorone diisocyanate (manufacturer: Hüls).
Grain distribution:
> 90 µm 3.6%
> 63 µm 33.8%
> 45 µm 58.1%
<45 µm 41.9%.
Melting start: approx. 123 ° C
Melt index (165 ° C; 2.16 kp load): approx. 16 g / 10 min according to DIN 53735.

Heating rollers used:

like example 1

Transfer carrier used:

like example 1.

Claims (15)

1. A process for the production of nets from hot-melt adhesive powder on a transfer carrier web, in which process the hot-melt adhesive powder is first squeegeeed into the net-shaped engraving of a rotating engraving roller and from there is transferred to the transfer carrier web that is partially guided around this engraving roller, with this transfer carrier web previously partially guided around a rotating heating roller and pressed onto the surface of the engraving roller via this heating roller, as a result of which the transfer carrier web is heated to a temperature above the start of melting of the melting powder,
characterized in that fine powder with a maximum of 10% grain proportions of more than 100 µm grain size is used for scraping into the engraving of the engraving roller, which fine powder is rotated immediately before being scraped into the engraving about an axis parallel to the engraving roller axis, and that the transfer carrier web by means of an elastic surface of the heating roller is pressed elastically onto the engraving roller, thereby further compacting the fine powder that has been scraped into its engraving. 2. The method according to claim 1, characterized in that fine powder is used, the grain proportions with a grain size of less than 90 microns is at least 95%. 3. The method according to claim 1, characterized in that copolyamides, copolyesters, polyethylenes, polyvinyl acetates and / or polyethylene vinyl acetates are used as fine powder. 4. The method according to claim 1, characterized in that hot-melt adhesive powders are used as fine powder, which begin to melt between 70 and 160 ° C, preferably between 80 and 135 ° C. 5. The method according to claim 4, characterized in that the melt index of the fine powder measured at 160 ° C and 2.16 kp load according to DIN 53735, at 1-200 g / 10 min, preferably at 5-100 g / 10 min. 6. The method according to claim 1, characterized in that a kraft paper with a weak silicone coating is used as the transfer carrier web. 7. Device for performing the method according to one or more of claims 1 to 6, with a rotating engraving roller, which has a net-shaped engraving on its outer surface, characterized in that the mesh-shaped engraving (7) of the engraving roller (6) has a release film coating. 8. The device according to claim 7, characterized in that the engraving roller (6) is coated with a Teflon film. 9. Apparatus for carrying out the method according to one or more of claims 1 to 6, with a heating roller pressing the transfer carrier web against the engraving roller, characterized in that the heating roller (4) has a flat structure temperature-resistant thermoplastic fibers arranged in several layers is wrapped. 10. An apparatus for performing the method according to one or more of claims 1 to 6 with a heat transfer roller adapting the transfer carrier web to the engraving roller, characterized in that the heat roller (4) has a silicone-containing coating (5) made of thermally conductive fillers in a thickness of 0 to 10 mm. 11. An apparatus for performing the method according to one or more of claims 1 to 6, with a doctor blade applied to the engraving roller for doctoring the hot-melt adhesive powder into the engraving of the engraving roller, characterized in that the doctor blade (13) is approximately tangential to the engraving roller (6 ) is present and that its coating edge is chamfered in such a way that a funnel-shaped filling gap is formed between it and the engraving roller. 12. An apparatus for performing the method according to one or more of claims 1 to 6, with a powder container, at the outlet opening facing the engraving roller a doctor blade is arranged, characterized in that in the powder container (12) immediately in front of the doctor blade edge a rotatable about its axis Stirring rod (15) is provided parallel to the engraving roller axis. 13. The apparatus according to claim 12, characterized in that the stirring rod (15) is provided on its circumference with radially projecting pins 16). 14. Hot melt adhesive networks produced by the process according to one or more of claims 1 to 6, characterized in that they do not crosslink under the influence of temperature. 15. Hot melt adhesive networks produced by the process according to one or more of claims 1 to 6, characterized in that they crosslink under the action of temperature.

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